Sheets of cardboard mat, glass and other materials are frequently cut to provide components having openings and/or perimeters of circular or elliptical (generally referred to as "oval") configuration. Such components are widely used for mounting and framing of pictures and the like.
Machines are known in the art, and are commercially available, for cutting planar workpieces to such shapes; exemplary is the device described in Pierce U.S. Pat. No. 4,112,793, issued Sept. 12, 1978. Although the device of the Pierce patent is highly effective for its intended purposes, it has an inherent drawback, attributable to the manner by which the cutting blade is mounted.
As is true of virtually all machines of the kind described in the Pierce patent, the blade, supported to permit it to freely swivel, is positioned to trail slightly behind the axis of pivoting, thereby enabling it to seek an appropriate approach angle. This arrangement is disadvantageous for several reasons.
Most significantly, such machines are not capable of cutting perfect ovals because the blade has a tendency to proceed in a straight line; the deviation from a true elliptical path is particularly noticeable when the minor axis of the shape is relatively small compared to its major axis. Secondly, the trailing blade tends to produce an oval that "leans"; that is, the major and minor axes are tilted slightly from those of a true Cartesian oval. Finally, such an arrangement results in indefiniteness in the starting and finishing points of the blade, often causing those points to be noncoincident, ultimately producing imperfections along the cut.
It is recognized that at least certain of the foregoing deficiencies can be overcome by dynamically orienting the blade so as to maintain its cutting axis constantly tangent to the elliptical path that is generated. A commercially available device that is intended to operate in that general manner utilizes a control arm, attached at one end to a pivotable cutter head, which rotates about and follows, at its opposite end, an oblong cam. The mechanism does not however produce true tangency at all points of the oval, and it is unsatisfactory for other reasons as well; perhaps most notably, it employs no associated support, instead being positioned for use simply by fastening it to a base board through the workpiece itself.
Accordingly, it is the broad object of the present invention to provide a novel combination, machine and method for cutting oval shapes in planar workpieces, which shapes are virtually free of distortion and of imperfections along the line of cutting.
A more specific object is to provide such a combination, machine and method in which the cutting axis of the blade or wheel employed is dynamically oriented so as to maintain true tangency to the cut line or score at all points therealong.
Another object of the invention is to provide a novel machine for cutting shapes in planar workpieces, which permits facile and effective clamping, and precise positioning, of the workpiece, and which permits accurate cutting of bevels from either the front or back of the workpiece, and convenient and accurate V-grooving thereof.
Another more specific object is to provide a novel clamping system affording the foregoing benefits, which is, in addition, of relatively uncomplicated design and construction, which does not intrude into the cutting space, and which imposes no load on the cutting mechanisms or on the support structure therefor.
An additional more specific object is to provide a novel cutting head and head assembly affording the foregoing benefits, which is, in addition, of relatively uncomplicated design and construction, and which is capable of readily disposing either of two blades in an optimal position for effective cutting of the workpiece.